[arm] Add manifest steps to base-images (#8271)

Related: #8164

infra/build/functions/base_images.py

@@ -110,6 +110,51 @@ def run_build(steps, images, tags=None, build_version=MAJOR_TAG):
                              use_build_pool=False)
 
 
+def get_images_architecture_manifest_steps():
+  """Returns steps to create manifests for ARM and x86_64 versions of
+  base-runner and base-builder."""
+  images = [f'{TAG_PREFIX}/base-builder', f'{TAG_PREFIX}/base-runner']
+  steps = []
+  for image in images:
+    steps.extend(get_image_push_architecture_manifest_steps(image))
+  return steps
+
+
+def get_image_push_architecture_manifest_steps(image):
+  """Returns the steps to push a manifest pointing to ARM64 and AMD64 versions
+  of |image|."""
+  arm_testing_image = f'{image}-testing-arm'
+  amd64_manifest_image = f'{image}:manifest-amd64'
+  arm64_manifest_image = f'{image}:manifest-arm64v8'
+  steps = [
+      {
+          'name': 'gcr.io/cloud-builders/docker',
+          'args': ['tag', image, amd64_manifest_image],
+      },
+      {
+          'name': 'gcr.io/cloud-builders/docker',
+          'args': ['pull', arm_testing_image],
+      },
+      {
+          'name': 'gcr.io/cloud-builders/docker',
+          'args': ['tag', arm_testing_image, arm64_manifest_image],
+      },
+      {
+          'name':
+              'gcr.io/cloud-builders/docker',
+          'args': [
+              'tag', 'manifest', 'create', image, '--amend',
+              arm64_manifest_image, '--amend', amd64_manifest_image
+          ],
+      },
+      {
+          'name': 'gcr.io/cloud-builders/docker',
+          'args': ['manifest', 'push', image]
+      },
+  ]
+  return steps
+
+
 def base_builder(event, context):
   """Cloud function to build base images."""
   del event, context
@@ -119,6 +164,10 @@ def base_builder(event, context):
   images = [TAG_PREFIX + base_image for base_image in BASE_IMAGES]
   run_build(steps, images)
 
+  steps = get_images_architecture_manifest_steps()
+  images = ['base-builder', 'base-runner']
+  run_build(steps, images)
+
   introspector_steps = _get_introspector_base_images_steps()
   introspector_images = [
       TAG_PREFIX + base_image for base_image in INTROSPECTOR_BASE_IMAGES